This invention relates to wheel end assembly, and more particularly to a wheel end assembly with a double reduction gear set for an inverted portal axle as used in a mass transit vehicle.
Mass transit vehicles, such as trolley cars, buses, and the like typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time during stops and facilitates boarding for all passengers, especially for elderly and disabled passengers as well as for children.
Mass transit vehicles typically have several axles that support, drive and steer the vehicle. Many such vehicles provide a rigid axle having an input positioned off-center near one wheel end to form an inverted portal axle configuration. The input to the portal axle rotates about a longitudinal axis and is typically low to the ground to allow the vehicle floor to be as low as possible. The output to the wheels defines a lateral axis that is vertically higher than the longitudinal axis for the input.
This inverted portal axle includes a short axle shaft member that drives the wheel end near the input and a long axle shaft member that drives the opposite wheel end. The portal axle further includes a pair of gear assemblies, one gear assembly positioned at each wheel end, to raise driving input from each of the axle shafts up to the vertically higher output position at the wheels. Typically, helical gear assemblies with idler gears are used to carry higher loads for smaller gears. Typically this gear assembly includes a gear housing, an input gear driven by the respective axle shaft, an output gear for driving the wheel, and a pair of idler gears in meshing engagement with the input and output gears.
The output gear drives a wheel shaft that is enclosed within a spindle that is mounted to the gear housing. A wheel hub is mounted for rotation relative to the spindle and receives driving input from the wheel shaft. A brake spider is also mounted to the gear housing to support a brake input member.
One disadvantage with the traditional configuration is that the inverted portal axle incorporates at least three bolted joints and four bearings to support the rotating components. Assembly time and overall component cost is significant due to the large number of components and complexity of this configuration. Also, the large number of components and the fasteners needed for the bolted joints increase the overall weight in the vehicle, which can significantly affect fuel economy.
Another disadvantage with the traditional configuration is that the ability to position the vehicle floor as close as possible to the ground is limited by the traditional helical gear assembly with idler gears. As described above, the input to the inverted portal axle is below the driving axis of rotation for the wheel ends. The helical gear assembly is used to transfer driving torque from the lower input position to the higher output position, as well as providing a desired gear reduction.
Traditionally, the helical gear assembly includes a helical pinion gear (input gear) that is operatively coupled to a ring and pinion gear at the axle input and a helical driven gear (output gear) that drives the associated wheel hub. A pair of idler gears is in meshing engagement with both the helical pinion and driven gears. This configuration, utilizing two (2) idler gears, can carry higher loads because there are two (2) tooth set contacts. However, this configuration is limited to close centerline mountings because the helical pinion gear and both idler gears are on the same centerline. Further, this configuration only provides a maximum of approximately 150 mm drop between the floor and the wheel centerline.
Accordingly, it is desirable to provide a gear assembly with required gear reduction that can easily be incorporated into an axle with non-concentric input and output components. Further, it is desirable to package this improved gear reduction assembly into an inverted portal axle configuration to provide an improved low floor profile to facilitate access to the vehicle. Additionally, it is desirable to provide a simplified wheel end assembly for an inverted portal axle configuration to reduce weight, cost, and assembly time in addition to overcoming the other deficiencies in the prior art discussed above.